// Copyright 2013 The Chromium Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

#include "cc/layers/scrollbar_layer_impl_base.h"

#include "cc/trees/layer_tree_impl.h"
#include "ui/gfx/geometry/rect_conversions.h"
#include <algorithm>

namespace cc {

ScrollbarLayerImplBase::ScrollbarLayerImplBase(
    LayerTreeImpl* tree_impl,
    int id,
    ScrollbarOrientation orientation,
    bool is_left_side_vertical_scrollbar,
    bool is_overlay)
    : LayerImpl(tree_impl, id)
    , scroll_layer_id_(Layer::INVALID_ID)
    , is_overlay_scrollbar_(is_overlay)
    , thumb_thickness_scale_factor_(1.f)
    , current_pos_(0.f)
    , clip_layer_length_(0.f)
    , scroll_layer_length_(0.f)
    , orientation_(orientation)
    , is_left_side_vertical_scrollbar_(is_left_side_vertical_scrollbar)
    , vertical_adjust_(0.f)
{
}

ScrollbarLayerImplBase::~ScrollbarLayerImplBase()
{
    layer_tree_impl()->UnregisterScrollbar(this);
}

void ScrollbarLayerImplBase::PushPropertiesTo(LayerImpl* layer)
{
    LayerImpl::PushPropertiesTo(layer);
    DCHECK(layer->ToScrollbarLayer());
    layer->ToScrollbarLayer()->set_is_overlay_scrollbar(is_overlay_scrollbar_);
    layer->ToScrollbarLayer()->SetScrollLayerId(ScrollLayerId());
}

ScrollbarLayerImplBase* ScrollbarLayerImplBase::ToScrollbarLayer()
{
    return this;
}

void ScrollbarLayerImplBase::SetScrollLayerId(int scroll_layer_id)
{
    if (scroll_layer_id_ == scroll_layer_id)
        return;

    layer_tree_impl()->UnregisterScrollbar(this);

    scroll_layer_id_ = scroll_layer_id;

    layer_tree_impl()->RegisterScrollbar(this);
}

bool ScrollbarLayerImplBase::SetCurrentPos(float current_pos)
{
    if (current_pos_ == current_pos)
        return false;
    current_pos_ = current_pos;
    NoteLayerPropertyChanged();
    return true;
}

bool ScrollbarLayerImplBase::CanScrollOrientation() const
{
    LayerImpl* scroll_layer = layer_tree_impl()->LayerById(scroll_layer_id_);
    if (!scroll_layer)
        return false;
    return scroll_layer->user_scrollable(orientation()) && clip_layer_length_ < scroll_layer_length_;
}

bool ScrollbarLayerImplBase::SetVerticalAdjust(float vertical_adjust)
{
    if (vertical_adjust_ == vertical_adjust)
        return false;
    vertical_adjust_ = vertical_adjust;
    NoteLayerPropertyChanged();
    return true;
}

bool ScrollbarLayerImplBase::SetClipLayerLength(float clip_layer_length)
{
    if (clip_layer_length_ == clip_layer_length)
        return false;
    clip_layer_length_ = clip_layer_length;
    NoteLayerPropertyChanged();
    return true;
}

bool ScrollbarLayerImplBase::SetScrollLayerLength(float scroll_layer_length)
{
    if (scroll_layer_length_ == scroll_layer_length)
        return false;
    scroll_layer_length_ = scroll_layer_length;
    NoteLayerPropertyChanged();
    return true;
}

bool ScrollbarLayerImplBase::SetThumbThicknessScaleFactor(float factor)
{
    if (thumb_thickness_scale_factor_ == factor)
        return false;
    thumb_thickness_scale_factor_ = factor;
    NoteLayerPropertyChanged();
    return true;
}

gfx::Rect ScrollbarLayerImplBase::ComputeThumbQuadRect() const
{
    // Thumb extent is the length of the thumb in the scrolling direction, thumb
    // thickness is in the perpendicular direction. Here's an example of a
    // horizontal scrollbar - inputs are above the scrollbar, computed values
    // below:
    //
    //    |<------------------- track_length_ ------------------->|
    //
    // |--| <-- start_offset
    //
    // +--+----------------------------+------------------+-------+--+
    // |<||                            |##################|       ||>|
    // +--+----------------------------+------------------+-------+--+
    //
    //                                 |<- thumb_length ->|
    //
    // |<------- thumb_offset -------->|
    //
    // For painted, scrollbars, the length is fixed. For solid color scrollbars we
    // have to compute it. The ratio of the thumb's length to the track's length
    // is the same as that of the visible viewport to the total viewport, unless
    // that would make the thumb's length less than its thickness.
    //
    // vertical_adjust_ is used when the layer geometry from the main thread is
    // not in sync with what the user sees. For instance on Android scrolling the
    // top bar controls out of view reveals more of the page content. We want the
    // root layer scrollbars to reflect what the user sees even if we haven't
    // received new layer geometry from the main thread.  If the user has scrolled
    // down by 50px and the initial viewport size was 950px the geometry would
    // look something like this:
    //
    // vertical_adjust_ = 50, scroll position 0, visible ratios 99%
    // Layer geometry:             Desired thumb positions:
    // +--------------------+-+   +----------------------+   <-- 0px
    // |                    |v|   |                     #|
    // |                    |e|   |                     #|
    // |                    |r|   |                     #|
    // |                    |t|   |                     #|
    // |                    |i|   |                     #|
    // |                    |c|   |                     #|
    // |                    |a|   |                     #|
    // |                    |l|   |                     #|
    // |                    | |   |                     #|
    // |                    |l|   |                     #|
    // |                    |a|   |                     #|
    // |                    |y|   |                     #|
    // |                    |e|   |                     #|
    // |                    |r|   |                     #|
    // +--------------------+-+   |                     #|
    // | horizontal  layer  | |   |                     #|
    // +--------------------+-+   |                     #|  <-- 950px
    // |                      |   |                     #|
    // |                      |   |##################### |
    // +----------------------+   +----------------------+  <-- 1000px
    //
    // The layer geometry is set up for a 950px tall viewport, but the user can
    // actually see down to 1000px. Thus we have to move the quad for the
    // horizontal scrollbar down by the vertical_adjust_ factor and lay the
    // vertical thumb out on a track lengthed by the vertical_adjust_ factor. This
    // means the quads may extend outside the layer's bounds.

    // With the length known, we can compute the thumb's position.
    float track_length = TrackLength();
    int thumb_length = ThumbLength();
    int thumb_thickness = ThumbThickness();
    float maximum = scroll_layer_length_ - clip_layer_length_;

    // With the length known, we can compute the thumb's position.
    float clamped_current_pos = std::min(std::max(current_pos_, 0.f), maximum);

    int thumb_offset = TrackStart();
    if (maximum > 0) {
        float ratio = clamped_current_pos / maximum;
        float max_offset = track_length - thumb_length;
        thumb_offset += static_cast<int>(ratio * max_offset);
    }

    float thumb_thickness_adjustment = thumb_thickness * (1.f - thumb_thickness_scale_factor_);

    gfx::RectF thumb_rect;
    if (orientation_ == HORIZONTAL) {
        thumb_rect = gfx::RectF(thumb_offset,
            vertical_adjust_ + thumb_thickness_adjustment,
            thumb_length,
            thumb_thickness - thumb_thickness_adjustment);
    } else {
        thumb_rect = gfx::RectF(
            is_left_side_vertical_scrollbar_
                ? bounds().width() - thumb_thickness
                : thumb_thickness_adjustment,
            thumb_offset,
            thumb_thickness - thumb_thickness_adjustment,
            thumb_length);
    }

    return gfx::ToEnclosingRect(thumb_rect);
}

} // namespace cc
